An electrolysis cell is a mechanical assembly for electrolyzing water to hydrogen and oxygen gas. To meet hydrogen and oxygen production requirements, a plurality of electrolysis cells are assembled in electrical series to form a cell stack. Referring to FIG. 1, each electrolysis cell comprises an anode catalyst 1, a cathode catalyst 3, an ion exchange membrane 5 disposed therebetween, an anode chamber 7, and a cathode chamber 9. During operation, water is introduced to the anode chamber 7 where it contacts the anode catalyst 1 and is electrolyzed to hydrogen ions, oxygen and free electrons. The hydrogen ions migrate through the ion exchange membrane 5 to the cathode catalyst 3 where they are recombined with the free electrons which flow through an external circuit 11 to the cathode catalyst 3, thereby producing hydrogen gas.
During hydrogen and oxygen gas production, some of the oxygen gas in the anode chamber 7 diffuses through the ion exchange membrane 5, escapes recombination with hydrogen on the cathode catalyst 3, and flows into the cathode chamber 9, thereby reducing the purity of the hydrogen gas. Similarly, a portion of the hydrogen gas in the cathode chamber 9 diffuses through the ion exchange membrane 5, escapes recombination on the anode catalyst 1, and flows into the anode chamber 7, thereby reducing the purity of the oxygen gas. Although this diffusion is minimal and the oxygen and hydrogen gases are substantially pure, typically only containing about 10 ppm to about 100 ppm contaminants, this purity is inadequate for many state-of-the-art applications such as hydrogen used for processing in the semiconductor industry, hydrogen utilized in the manufacture of artificial diamonds, and hydrogen utilized as a carrier gas in flame ionization equipment, among others. These applications require very high quality oxygen and hydrogen gases, typically exceeding about 99.999%. This purity level is one order of magnitude greater than the purity of hydrogen and oxygen produced in commercially available water electrolysis cells.
Consequently, attainment of high purity oxygen and hydrogen gases has been addressed by installing purification equipment downstream of the water electrolyzer. An example of such a device is a palladium separator which allows only the hydrogen molecules to pass. Other devices, such as deoxygenation units and recombiners, remove oxygen and hydrogen respectively. Although the desired purity is obtained with these devices, system complexity, reliability, and costs are negatively impacted.
What is needed in the art is an improved electrolysis cell capable of consistently producing high purity hydrogen and oxygen gases having a purity of about 99.999% or greater.